1. Field of the Invention
The invention relates to a gas-liquid chromatographic apparatus and a quick, accurate field test method for determining the final boiling point of a gasoline or other volatile liquid fraction.
2. Description of the Prior Art
Petroleum products, among others, must meet certain specifications before they can be marketed. An important specification, which is strictly enforced by Federal and State law, pertains to the final boiling point of the product and takes the form of an upper limit. The importance can be readily understood by considering that the Final Boiling Point of a product such as gasoline will markedly change if the gasoline becomes contaminated with other products such as kerosene or diesel fuels. The possibility of contamination exists since gasoline is distributed by pipeline, which may have previously been used to transport other products. Thus, certification that a gasoline meets specifications at a refinery exit, for example, does not insure that the product will meet specifications at the point of sale.
Current experimental methods used for the determination of the final boiling point of petroleum fractions employ distillation, however, simulated distillations such as by chromatographic means are also used. Interestingly, both of these methods are directed toward producing the entire boiling point distribution of the product, rather than just determining the final boiling point.
A method for the determination of the boiling distribution of a petroleum product by actual distillation is described by ASTM test D86-67. Briefly, a sample of the product is distilled under prescribed conditions and systematic observations of thermometer readings and volumes of condensate are made. The boiling point distribution must then be calculated from the observed readings.
Chromatography, which is also used to produce boiling point distributions, can be broadly defined as a technique for the separation and identification of chemical compounds. More specifically, it may be described as a process in which the components of a mixture are separated from one another by volatilizing a sample of the mixture into a carrier gas stream which is passed through and over a bed of packing generally comprising a 20 to 200 mesh solid support. The surface of the solid support is usually coated with relatively nonvolatile liquid, giving rise to the term gas-liquid chromatography. Different components move through the bed at different rates and so appear one after another at the effluent end of the bed where they are detected and measured by thermal conductivity changes, density differences or ionization detectors.
Methods for the determination of boiling point distributions by chromatography are described by ASTM test D2887-73 or U.S. Pat. No. 3,169,389. Briefly, the methods involve using: a chromatograph to resolve an unknown mixture of compounds into fractions having similar boiling points; a recorder to produce a graphical representation of the amount of each fraction as detected by a suitable means; and an integrator to produce a record of the cumulative amount of each of the fractions. Boiling point temperatures are assigned at various intervals as determined by previous experiment using a standard mixture containing materials of known boiling point. As presently practiced, these chromatographic methods are capable of producing a boiling point distribution, however they require the use of sophisticated equipment and techniques. Gas-liquid chromatographic columns and detectors must be capable of certain resolution, columns must be temperature programmed at reproducible rates, certain peaks must be identified, and precise calculations must be made.
It is readily observed that due to the complexity of the above mentioned methods for the determination of boiling point distributions, they are considered to be unsuitable for use in any environment other than a well-equipped laboratory. Thus, since final distribution terminals or points of sale of petroleum products are not usually characterized as containing such facilities, the need exists for a simple test which can be used outside of the laboratory to find the final boiling point of volatile hydrocarbon fractions.